Acoustic microscopy applied to nonlinear characterization of biological media.

The use of an acoustic microscope as a method for nonlinear characterization of biological media is evaluated. The method consists of measuring the second harmonic signal generated in a sample located at the focus of the acoustic lens. Two experimental configurations were compared: The first is the simple case where the sample is a liquid mixture filling the space between the lens cavity and the receiver; in the second case, the liquid mixture is confined to a thin layer at the focal plane, in order to simulate a real tissue layer. Aqueous solutions of ethylene glycol and methanol were used as liquid samples. Simple theoretical models are presented for each configuration and the predictions show good qualitative agreement with experimental measurements. These results confirm our belief that the acoustic microscope is potentially a good tool for nonlinear B/A imaging of biological systems.